Reyaad Khan (centre) appeared in an Isis recruitment video in 2014 YouTube

The RAF killed an Islamic State (Isis) militant from Cardiff with a drone strike as the jihadist was a threat to British security, David Cameron has revealed. The prime minister told MPs that the strike against the 21 year old in Syria was an "act of self-defence", and that he authorised the attack.

"If there is a direct threat to the British people and we are able to stop it by taking immediate action, then as prime minister I will also be prepared to take that action," he said in the House of Commons on 7 September. Cameron said Khan, who has appeared IS propaganda videos, was plotting terror attacks against the UK and "specific and barbaric" assaults on the West.

"We should be under no illusions – their intentions were the murder of British citizens," Cameron told the chamber. "In act of self-defence and after meticulous planning, Khan was killed in a precision air strike carried out on the 22 August by RAF remotely controlled aircraft."

The prime minister also told MPs that there were no civilian casualties from the strike and he took the decision as there was no other alternative. "In this area there is no government we can work with and we have no military on the ground to detain those making plots," he explained.

The Tory leader stressed the assault was not part of the wider coalition attacks on IS in Syria and Iraq, instead it was a specific attack on a terrorist threat. "I've been absolutely clear that the government will return to this house for a separate vote if we propose to join coalition strikes in Syria," he said.

Elsewhere, a US drone strike killed another British IS militant, Junaid Hussain, according to Cameron. Hussain was a computer hacker who joined the terror group in 2013. He was killed in the Syrian city of Al-Raqqa on 24 August by the US forces, the PM said.

The comments came just minutes after Cameron promised the UK would take up to 20,000 more Syrian refugees over the course of the parliament, which will come to an end in May 2020. The prime minister confirmed that some of the UK's foreign aid budget will be used to help the refugees, who are fleeing the Middle East for Europe.

Cameron said Britain had a "moral responsibility" to resettle the people and would accept more refugees under the UN's schemes. "Given the scale of the crisis and the suffering of the Syrian people, it's right that we should do much more," he added.

The prime minister made the statement after increasing pressure on his government over the refugee crisis, with Cameron being criticised for previously claiming the UK did not need to take in more Syrian refugees.